Within Task Learning versus Previously Acquired Knowledge

An important issue regarding the category representations of infants is whether they are constructed (presumably on the basis of real-life experience) before the experiment began or whether the category representations are formed on-line, during the course of an experiment (Mareschal & Quinn, 2001). The former view would argue that infants recognize the photographs as representations of objects in the world with which they are already familiar and for which they have previous category knowledge. By this view, the familiarization phase of the familiarization/novelty-preference procedure would serve to prime the knowledge that the infants have already acquired outside the laboratory.

The latter view would have it that the format of the familiarization/novelty-preference procedure better lends itself to an interpretation that can be understood in terms of category formation. Infants are presumed to construct the category representation as more and more exemplars from the familiar category are presented (Mareschal, French, & Quinn, 2000). Even by this reasoning, however, it is difficult to completely rule out the possibility that knowledge access does not facilitate the performance of the participating infants. Consider, for example, 3- to 4-month-olds presented with cats or horses and then tested with exemplars from contrasting animal categories such as birds, dogs, tigers, giraffes, and zebras. Given that young infants are not likely to have observed (at least directly) animals such as giraffes or zebras or the particular cat and horse exemplars to be presented in the task, one might be tempted to say that the participating infants rely exclusively on perceptual processing, and that they are forming the category representations during the course of the familiarization trials. However, parents are known to read to their infants from picture books that may contain pictorial exemplars of animals. In addition, even young infants may be able to recognize that animals like giraffes and zebras are more like other animals that they do know about (e.g., humans) than furniture items (Quinn & Eimas, 1998). Thus, even in an experiment that is designed as a study of concept formation, it is possible that young infants may recruit from a preexisting knowledge base that at least in part determines their preference behavior.

This issue of whether the experiments are investigations into category formation or possession has been addressed in two ways. First, because a number of studies conducted by Quinn and collaborators have investigated whether infants form separate category representations for cats and dogs, it is possible to compare the categorization performance of infants that have been exposed to pets at home with those that have not. A variety of analyses have been performed, and none have revealed a facilitative effect of a home pet on categorization performance. These null results thus fail to support the suggestion that infant categorization of nonhuman animals in the laboratory is assisted by real-world experience with nonhuman animals occurring prior to arrival at the laboratory.

Another way to think about perceptual process and knowledge access as contributors to infant categorization performance is to argue that if infants have preformed representations for nonhuman animal species that are simply tapped into as a basis for performance during an experiment conducted with the familiarization/novelty-preference procedure, then it should prove difficult to manipulate categorization performance via perceptual perturbations to the stimuli. That is, via knowledge access, cats should be recognized as cats and dogs should be recognized as dogs. However, a series of experiments has shown that infant categorization performance for classes of cats and dogs can be manipulated. This was possible because of an asymmetry in categorization performance that was detected in the initial investigation of Quinn et al. (1993). Although infants familiarized with cats displayed a novelty preference for dogs compared with novel cats, infants familiarized with dogs did not display a preference for cats over novel dogs. In other words, infants familiarized with cats formed a category representation for cats that included novel cats, but excluded dogs, whereas infants familiarized with dogs formed a category representation for dogs that included both novel dogs as well as cats.

In follow-up investigations, it was demonstrated that the cat versus dog category asymmetry could not be explained via a spontaneous preference for dogs: Infants presented with cats versus dogs without prior familiarization did not have an a priori preference for the dogs (Quinn et al., 1993). However, through a combination of typicality ratings obtained from adults, computational modeling, and further experimentation with infants, the initial asymmetry was shown to reflect the fact that the dogs were more variable than the cats, causing the cats to be subsumed under the broader class of dogs (Mareschal et al., 2000; Quinn et al., 1993). In one experiment conducted with 3- to 4-month-olds, when the variability of the dog class was reduced, presumably removing the inclusion relation of cats within dogs, the asymmetry was removed (Quinn et al., 1993). In another experiment carried out with same age group, the inclusivity relation of the categories was reversed through a combination of stimulus selection and image processing, and the asymmetry was reversed: the infants formed a category representation for cats that included dogs, and a category representation for dogs that excluded cats (French, Mermillod, Quinn, & Mareschal, 2001). These studies of categorization cats versus dogs by young infants make the important point that at least in the case of nonhuman animals, the infants are forming their category representations over the course of the familiarization trials, rather than tapping into preexisting concepts that had been formed prior to arriving at the laboratory.

Finding Your Confidence

Finding Your Confidence

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